The number of protons in He is 2.
Explanation:
Atomic number refers to the number of protons in the nucleus of an atom.
He is a noble gas whose atomic number is 2.
Therefore, the number of protons in the nucleus of He is 2.
Also, the number of neutrons in the nucleus of He is 2
And mass number is the sum of protons and neutrons present in the nucleus of an atom.
Therefore, mass number of He = 2 + 2 = 4
